It is known that there is an increasing need to alter the setting of chair, armchair and similar seats in relation to the various positions assumed by the user throughout the day. In the office environment particularly, following the widespread introduction of computer and word processing systems on desks, it is necessary to provide a chair enabling a comfortable and ergonomically correct position to be achieved both when writing normally at a table or desk and when using a computer keyboard. The keyboard usually is placed in a lower position relative to the desk top so that it is necessary to provide a slight backward tilt to the so-called active rest position.